The evaluation of myocardial perfusion and metabolism plays an important role in the diagnosis and treatment of all types of heart disease. Noninvasive techniques that could make such determinations utilizing standard external imaging devices would enhance the availability of patient studies and potentially reduce their cost. Therefore, the long-term objectives of this study are to develop a better understanding of the basic characteristics of radionuclide compounds that can assess myocardial blood flow and functional state. The specific aims of this study are to evaluate the myocardial uptake, washout, extraction and compartmental distribution of a radioiodinated fatty acid analogue [15-(p-Iodophenyl)-3-(R,S)Methylpentadecanoic Acid (beta-MPDA)] and thallium-201 in an isolated rabbit heart model during varied levels of coronary perfusion and alterations in cellular metabolism. In other experiments the extraction and lipid pool distribution of beta-MPDA will be compared to that of palmitate, a naturally occurring free fatty acid. In these studies both buffer and blood perfused hearts will be employed having either constant flow or perfusion pressure respectively. Arterial and coronary venous samples are collected at timed intervals and are subsequently measured to determine myocardial isotope uptake, clearance and extraction. Special chemical separation techniques will be used to analyze the distribution of isotope in heart tissue. The medical significance of this work will be that the results obtained from this basic research will provide the information needed to understand the cardiac kinetics of thallium and beta-MPDA. This information can then be used to formulate the methods for myocardial imaging of the fatty acid analogue alone, and in combination with thallium perfusion imaging. These methods would be likely to attain widespread clinical utility.